Transmission
Smallpox is highly contagious. In most cases, people get smallpox by inhaling droplets of saliva, which are full of virus, during face-to-face contact with an infected person. When someone becomes infected, they do not immediately feel sick or shed virus to their household contacts. In addition, they have no symptoms for 10 to 12 days. After the virus has multiplied and spread throughout the body, a rash and fever develop. This is the "illness" portion of the disease, and it's when someone is most infectious.
Some risk of transmission lasts, however, until all scabs have fallen off. Contaminated clothing or bed linens also can spread the virus. Those caring for people with smallpox need to use special safety measures to ensure that all bedding and clothing from the infected person are cleaned appropriately with bleach and hot water. Caretakers can use disinfectants such as bleach and ammonia to clean contaminated surfaces.